The present invention relates to a double lumen continuous flow hemodialysis catheter.
Dialysis is a filtration process to separate crystalloid from colloid substances (or smaller molecules from larger ones) in a solution by interposing a semipermeable membrane between the solution and water. The crystalloid substances or smaller molecules pass through the membrane into the water on the other side. The colloids do not. Hemodialysis is the dialysis of soluble substances and water from the blood by diffusion through semipermeable membrane. Separation of cellular elements and colloids from soluble substances is achieved by differential pore size in the membrane and rates of diffusion.
A hemodialysis unit is connected to a patient""s body by means of a catheter. The catheter is inserted partially within the body with its distal end placed in a blood vessel and its proximal end connected to the hemodialysis unit. The catheter can be a rigid metal device such as a needle or a flexible plastic device such as a cannula. A double lumen catheter has two lumens that allow both irrigation and aspiration. For example, a double lumen catheter can be used for removing blood from a fistula or vein for processing in the hemodialysis machine and for returning the processed blood back to the fistula or vein.
During hemodialysis, a patient""s blood flows through the catheter to an extracorporeal circuit consisting of blood lines and the hemodialysis unit. The unit provides and controls the flow of blood. Inside the unit, blood passes the inner lumens of thousands of capillary membranes. Uremic toxins accumulated in the patient""s blood diffuse through the membrane while blood cells and proteins are retained. Outside the membranes, a constant flow of dialysate (an aqueous solution containing physiologic salts) removes the uremic toxins. At the same time, water is extracted from the patient""s blood by ultrafiltration and purified blood is channeled back into a body by means of the catheter.
A hemodialysis patient""s blood must be adequately and completely treated. A number of medically adverse effects result from incomplete elimination of toxins. Performance of a hemodialysis unit is affected by factors related to the patient""s vascular access such as degree of access recirculation, cardiopulmonary recirculation, access flow and suction pressure developed by the hemodialysis blood pump as it pulls blood into the extracorporeal hemodialysis circuit. See Keshaviah, U.S. Pat. No. 5,507,723. Parameters that may be varied to achieve adequate hemodialysis include blood flow rate, dialysis solution flow rate, dialyzer competency and temperature. Generally, raising blood flow rate increases dialyzer clearance of small molecular weight solutes. Consequently, higher blood flow rates have been used to improve dialysis clearance efficiency. However, conditions such as access recirculation decrease clearance. Access recirculation is the recirculation of treated blood back into the hemodialyzer system. Access recirculation reduces clearance of solutes and causes inadequate dialysis. Recirculation reduces the effective blood flow and diminishes the efficiency of the hemodialysis process. Generally blood recirculation values of more than 15 percent are unacceptable.
Changes in catheter design have been suggested for the purpose of reducing access recirculation. Apertures of intake and outflow lumens have been longitudinally spaced 20-30 mm apart to prevent recirculation. For example, Twardowski et al. U.S. Pat. No. 5,569,182 discloses that the lumen for outflow of blood back into the vein should terminate beyond the lumen for inflow. The purpose of this is to prevent cleansed blood from reentering the blood outlet needle and returning to the dialysis machine. However, longitudinal spacing of the apertures in of itself, does not adequately diminish access recirculation.
There remains a need for a double lumen catheter that addresses problems of access recirculation and inadequate flow rates.
The invention relates to a double lumen catheter that accommodates increased flow rates and minimizes access recirculation. The catheter comprises an elongated tube that has unitary outer walls. A longitudinal planar septum divides the interior of the tube into an inlet lumen and a longer return lumen. The inlet lumen extends from a proximal end of the tube to an end terminating in a distally forward facing aperture. The return lumen extends contiguously with the inlet lumen from the proximal end of the tube to an end terminating in a distally forward facing aperture spaced in the longitudinal direction distally forward of the inlet lumen aperture. A diverting structure extends from an outer wall of the return lumen distally forward of the aperture of the inlet lumen. The diverting structure diverts flow of treated fluid discharged from the return lumen away from the distally forward facing aperture of the inlet lumen.
The invention also relates to a blood purification system, comprising a dialysis unit for purifying a patient""s blood and a dual lumen catheter with diverting structure coupled to a dialysis unit.
In a final aspect, a method is provided for circulating blood through the double lumen catheter wherein blood is withdrawn from a vein through the inlet aperture of the inlet lumen and after treatment is discharged by means of the catheter back into the vein through the aperture of the return lumen. Blood discharged from the catheter is diverted away from the aperture of the inlet lumen.